Pet's sound when satisfied it's lifted bone (7)
I believe the answer is:
stirrup
'bone' is the definition.
(bone of the ear)
'pet's sound when satisfied it's lifted' is the wordplay.
'pet's sound' becomes 'purr' (I've seen this in another clue).
'when satisfied' becomes 'its' (I can't justify this - if you can you should believe this answer much more).
'it's lifted' says the letters should be written in reverse (going up in down clue).
'purr'+'its'='purrits'
'purrits' back-to-front is 'STIRRUP'.
Can you help me to learn more?
(Other definitions for stirrup that I've seen before include "Small thing needed in hearing" , "Rider's footpiece" , "Small bone of the middle ear - it purrs (anag)" , "Rider's foot loop" , "In which a rider's foot rests" .)